Method for sub-atmospheric gas delivery with backflow control

Abstract

A sub-atmospheric gas delivery system ( 100 ) with a backflow control apparatus ( 10 ) for preventing backflow into the sub-atmospheric gas source ( 14 ). The gas delivery system includes three fluidly coupled sticks: a purge stick ( 120 ), a process gas delivery stick ( 124 ) and an evacuation stick ( 130 ). The backflow control apparatus comprises a gas line ( 26 ) fluidly coupling the sub-atmospheric gas source to a chamber ( 50 ), a valve ( 20 ) attached to the sub-atmospheric gas source for blocking fluid communication between the gas source and the gas line upon receipt of a first signal, a flow restrictor (R) in fluid communication with the gas line and positioned between the valve and the chamber, and first and second pressure transducers (P 1 and P 2 ) in fluid communication with the gas line and positioned on either side of the flow restrictor. Each transducer is capable of generating a signal representative of pressure. The backflow control apparatus further includes a valve controller unit ( 40 ) connected to the first and second pressure transducers and the valve. The controller is capable of generating the aforementioned first signal in response to the signals from the first and second pressure transducers.

What is claimed is:  
     
       1. In a gas delivery system, a method of preventing backflow into a source of sub-atmospheric gas having a valve, wherein the sub-atmospheric gas source and the chamber are fluidly coupled by a gas line having a flow restrictor therein, the method comprising the steps of: 
       a) measuring a first pressure in the gas line between the sub-atmospheric gas source and the flow restrictor;  
       b) measuring a second pressure in the gas line between the flow restrictor and the chamber;  
       c) comparing said first pressure to said second pressure; and  
       d) closing the valve when said second pressure exceeds said first pressure.  
     
     
       2. A method according to claim  1 , wherein said step 
       a) includes generating a first signal representative of said first pressure, said step  
       b) includes generating a second signal representative of said second pressure, and said step c) includes comparing said first and second signals.  
     
     
       3. A method according to claim  2 , wherein said step 
       d) includes generating a third signal to actuate said closing of the valve.  
     
     
       4. A method of preventing backflow of a second gas into a sub-atmospheric source of a first gas comprising the steps of: 
       a) measuring the temperature vs. time characteristics of the sub-atmospheric source of the first gas;  
       b) comparing said measured temperature vs. time characteristics to a predetermined temperature vs. time characteristics corresponding to an exothermic reaction representative of a backflow of the second gas into the sub-atmospheric source of the first gas; and  
       c) closing off the sub-atmospheric source of the first gas based on a comparison of said measured temperature vs. time characteristics to said predetermined temperature vs. time characteristics.  
     
     
       5. A method according to claim  4 , wherein said temperature vs. time characteristics comprise a single temperature value and said predetermined temperature vs. time characteristics comprise a single threshold value.